1. Field of the Invention
The present invention relates to a piezoelectric resonator in which a tuning-fork piezoelectric resonator element made of, for example, quartz crystal or the like is housed in a casing, and to a manufacturing technique thereof.
2. Description of the Related Art
Conventional piezoelectric resonators include a tuning-fork quartz-crystal resonator adopted as a signal source or the like which keeps pace of a watch. Being small in size, low in cost, and low in power consumption, the tuning-fork quartz-crystal resonator is very effective as a piezoelectric resonator mounted in a small electronic device such as a watch and is coming into use in wider applications. FIG. 9(a) to FIG. 9(c) show an example of this conventional tuning-fork quartz-crystal resonator. The tuning-fork quartz-crystal resonator is structured such that a tuning-fork quartz-crystal resonator element 100 shown in FIG. 9(a) is mounted in a casing 120 shown in FIG. 9(b) via a conductive adhesive 122.
The quartz-crystal resonator element 100 has a base portion 101 and two (pair of) oscillating arms 102 which are set parallel with each other at a predetermined interval and extend in one direction from the base portion 101. In the drawings, 105a and 105b denote groove portions formed in one surface and a rear surface of each of the oscillating arms 102 to enhance oscillation efficiency and reduce a power loss, 106 denotes excitation electrodes exciting tuning-fork oscillation based on bending oscillation in the groove portions 105a, 105b and peripheral areas thereof, 107 denotes lead electrodes, and 120a denotes a cover mounted on the casing 120 to seal it.
In such a quartz-crystal resonator, adjustment films 108 are formed for frequency adjustment on tips of the oscillating arms 102. The adjustment films 108 are formed so as to be apart from the excitation electrodes 106, and as shown in FIG. 9(c), are shaved for the adjustment of thickness and area thereof by, for example, laser irradiation by a laser irradiator 30. However, when the adjustment films 108 are shaved, shavings of the adjustment films 108 scatter and adhere to the excitation electrodes 106 to cause a short-circuit of the excitation electrodes 106, which involves a risk that the quartz-crystal resonator may become a defective product.
To solve this problem, there has been conventionally proposed the following methods. For example, patent document 1 describes a quartz-crystal resonator element in which an excitation electrode and an adjustment film are provided on a tuning-fork quartz-crystal piece and a high-melting point scattering prevention film is formed so as to cover the excitation electrode and the adjustment film. In this quartz-crystal resonator, the adjustment film is melted by laser to be shaved, and the scattering prevention film prevents the adjustment film from scattering at the time of the frequency adjustment. Further, the adjustment films, even if scattering toward the excitation electrode side, adheres onto the scattering prevention film, which can prevent the short-circuit of the excitation electrode. Then, shavings of the cut adjustment film are discharged from a hole that the laser forms in the scattering prevention film. However, forming the scattering prevention film in the quartz-crystal resonator element increases the number of element manufacturing processes and makes the element one size larger, leading to a size increase of the quartz-crystal resonator itself.
Further, patent document 2 describes a quartz-crystal resonator in which, in order to prevent a quartz-crystal resonator element from chipping due to the collision of its oscillating ends with a wall portion of a casing, projecting portions are provided on an upper surface and a lower surface of the casing so that an upper surface and a lower surface of the quartz-crystal resonator element except its tip portion come into contact with the projecting portions. The quartz-crystal resonator of the patent document 2 can prevent chipping of a quartz-crystal piece which becomes the element, but gives no description regarding the prevention of the adhesion of shavings of adjustment films. Therefore, the quartz-crystal resonator of the patent document 2 also involves a risk of becoming a defective product due to the aforesaid problem.    [Patent Document 1] Japanese Patent Application Laid-open No. 2000-223998 (paragraph No. 0019, 0020)    [Patent Document 2] Japanese Patent Application Laid-open No. 2003-133883 (paragraph No. 0011)